The influence of various pharmacological agents on the spontaneous and electrically-induced release of amino acid transmitters has been studed in rat cerebral cortex slices. Ouabain and K ion maximally accelerate the spontaneous release of labeled gamma-hydroxybutyrate and glutamate from preloaded slices, and concommitantly prevent their release with electrical stimulation. Pentobarbital blocks the accelerating effects of these agents and restores release with electrical stimulation. Pentobarbital alone enhances the electrically-induced release of GABA and competitively inhibits its reuptake, while the barbiturate has no influence on these same parameters of glutamic acid transport, illustrating the differential effect of an anesthetic agent on an inhibitory and an excitatory amino acid. The same problems of amino acid transmitter release are under study in vivo utilizing a newly developed method for perfusion of the rat spinal cord, combined with stimulation of dorsal and ventral roots. Active transport of glycine from spinal fluid to blood has been identified and characterized.